Try opening the game again, note the time, then check the system log and see if you can work out why its not starting. It might tell you whether or not its checking for a 1GHz (and/or a G4) CPU and quitting when it doesn't find it. Or it might indicate that its just trying and failing.

When you install the new drive, it might be worth trying out the old swapfile partition trick. Might compensate for the lack of RAM a bit. A clean install might also help. Depends how used the current one is.

I wonder whether its worth trying to overclock the graphics chip. I would be careful doing this with that iBook, its likely within the serial number bracket for a potentially ropey logic board. The recall program was due to faulty video chips, so it may be unwise to antagonise it. Unless its under three years old.....

PM me the serial number if you want me to check on that. Might also be able to tell you if its had a new board already. Not that that makes OC'ing the GPU any safer.

I would definitely max out the RAM too.